In recent years, there is proposed a light emitting unit 62 as shown in FIG. 18 (see, e.g., Japanese Patent Application Publication No. 2011-108808). The light emitting unit 62 disclosed in JP2011-108808A includes a light emitting module 61 and a box-shaped cover member 60 covering the outside of the light emitting module 61.
The light emitting module 61 includes a light source unit 64 and a clad member 65 for covering the light source unit 64. The clad member 65 is made of a silicon resin.
The light source unit 64 includes a substantially rectangular substrate 66, a light emitting element 63 mounted on the substrate 66 and lead members 67 as lead wires.
The light emitting element 63 includes a package body 63a made of ceramic, an LED chip (not shown) mounted on the package body 63a and a light-transmitting molding resin which encapsulates the LED chip. The light emitting element 63 is supplied with electric power through the lead members 67.
The lead members 67 are soldered to the positive terminal portion, the negative terminal portion and the return wiring terminal portions formed in the wiring pattern on the substrate 66. The lead members 67 are led out from the opposite sides of the substrate 66.
The clad member 65 is formed into a rectangular parallelepiped shape and is provided with protrusion portions 65a from which the lead members 67 are led out.
The cover member 60 has an opening formed at one surface side thereof (at the rear side of the drawing sheet in FIG. 18). Notch portions (not shown) each having a generally U-like shape are formed in the opposing side walls existing at the opening side of the cover member 60. The protrusion portions 65a of the clad member 65, from which the lead members 67 are led out, are fitted to the notch portions.
Attachment tongue pieces 60b extending outward are formed on a diagonal line at the opening side of the opposing side walls having the notch portions. The cover member 60 is in the form of 180 degree rotation symmetry. Screw holes, through which attachment screws are inserted, are formed in the attachment tongue pieces 60b. 
There is also proposed a light emitting unit as shown in FIG. 19 (see, e.g., Japanese Patent Application Publication No. 2011-124327). The light emitting unit disclosed in JP2011-124327A includes a light emitting module 261 and a box-shaped case 270 covering the outside of the light emitting module 261.
The light emitting module 261 includes a light source unit 264 and a frame-like seal member 269 made of a silicon resin and arranged to surround the outer periphery of the light source unit 264.
The light source unit 264 includes a substantially rectangular substrate 266, a light emitting element 263 mounted on the substrate 266 and lead members 267 as lead wires. The light emitting element 263 includes a package body (not shown) made of ceramic, an LED chip (not shown) mounted on the package body and a light-transmitting molding resin which encapsulates the LED chip.
The seal member 269, which has a rectangular frame shape, is formed larger than the outer periphery of the substrate 266. A pair of protrusion portions 269a, from which the lead members 267 are led out, is formed in the two opposing sides of the seal member 269.
The case 270 includes a box-shaped base case member 271 having an opening 271a and a box-shaped cover case member 272 having an opening 272a. In this light emitting unit, the seal member 269 is interposed between, and gripped by, the end portion of the base case member 271 existing at the side of the opening 271a and the end portion of the cover case member 272 existing at the side of the opening 272a. 
The base case member 271 includes an attachment piece 271b having a screw hole through which an attachment screw 268 is inserted.
The cover case member 272 is made of a transparent acryl resin so that the light emitted from the light emitting element 263 can transmit the cover case member 272. A convex portion 272c protruding in a dome-like shape is formed in the portion of the cover case member 272 opposing the light emitting element 263. In the cover case member 272, an attachment tongue piece 272b having a screw hole through which an attachment screw 268 is inserted is formed in a position corresponding to the attachment piece 271b of the base case member 271. The height of the cover case member 272 is set a little larger than the height of the base case member 271.
In the light emitting unit 62 disclosed in JP2011-108808A, the protrusion portions 65a are formed in the opening-side central areas of the opposing side walls of the cover member 60. The attachment tongue pieces 60b are arranged at the opposite sides from each other with respect to the centerline interconnecting the protrusion portions 65a of the cover member 60 when seen in a plan view. Therefore, it is difficult to reduce the size of the light emitting unit 62 in the transverse direction orthogonal to the centerline when seen in a plan view.
In the light emitting unit 62 shown in FIG. 18, there are four lead members 67 respectively connected to the positive terminal portion, the negative terminal portion and the return wiring terminal portions formed in the wiring pattern on the substrate 66. Electric power is supplied to the light emitting element 63 through the lead members 63. It is therefore likely that a power loss may be generated in the light emitting unit 62 due to the voltage drop caused by the wiring pattern between the return wiring terminal portions on the substrate 66.
In the light emitting unit of the configuration shown in FIG. 19, the convex portion 272c protruding in a dome-like shape is formed in the portion of the cover case member 272 opposing the light emitting element 263. The convex portion 272c serves as a lens portion. This makes it possible to efficiently extract the light emitted by the light emitting element 263 from the case 270.
In the light emitting unit of the configuration shown in FIG. 19, however, a demand exists to further enhance the light utilization efficiency.